Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Changes in threshold voltage of the cells, through programming of a charge storage structure (e.g., a floating gate or charge trap), or other physical phenomena (e.g., phase change or polarization), determine the data state of each cell. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, cellular telephones, and removable memory modules, and the uses for flash memory continue to expand.
Flash memory typically utilizes one of two basic architectures known as NOR flash and NAND flash. The designation is derived from the logic used to read the devices. In NOR flash architecture, a logical column of memory cells is coupled in parallel with each memory cell coupled to a data line, such as those typically referred to as bit lines. In NAND flash architecture, a column of memory cells is coupled in series with only the first memory cell of the column coupled to a bit line.
The demand of higher density and larger page/word parallelism in memory devices results in an increasing number of circuits that are repeated on a die many times. Such circuits include, by way of example only and not by way of limitation, sense amplifiers, page buffers, program load registers, and the like. As the density of flash memory devices continues to increase, the tolerances for components, including the repeated circuits, in memory devices drops.
Many memory devices use matched circuits for such things as sense amplifiers, current mirrors, and the like. As the components of memories continue to decrease in size and as memory devices continue to increase in density, current margins for matched circuits also shrink. Matching is, in part, a function of the circuit area, with increased ability to match circuits leading to increased area of the components of the circuit. With current margins shrinking, matching smaller circuits is increasingly difficult.
For the reasons stated above, and for other reasons which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for improved matching in memory device circuitry.